Preparation of multi-hapten mutant g6pdh conjugates and their use for detection of multiple analytes

ABSTRACT

The present invention relates to multi-hapten mutant G6PDH conjugates, methods of their preparation and their use for detection of multiple analytes. The compositions of the invention comprise different types of haptens (molecules) require to be immobilized into the G6PDH to make one multi-hapten-G6PDH conjugate. Both thiol and amine functional groups on G6PDH are utilized for immobilization of different haptens.

The present invention relates to multi-hapten mutant G6PDH conjugates,methods of their preparation and their use for detection of multipleanalytes.

In the field of in-vitro diagnostics, homogeneous immunoassays, such asEnzyme multiplied immunoassay technique (EMIT)-assays are used to detectanalytes, in particular, drugs of abuse in samples of subjects to betested. For example, the documents U.S. Pat. No. 6,455,288, U.S. at. No.6,033,890, U.S. Pat. No. 6,090,567 describe methods for immunoassay ofanalytes employing glucose-6-phosphate dehydrogenase (G6PDH) enzymes aslabels.

The principle of the EMIT®assay arises from the competitive binding andinteraction between an analyte analog conjugate to G6PDH and freeanalyte in a patient sample to the free antibody. This results incompetition between analyte in the sample and analyte- or analyteanalog-labeled with glucose-6-phosphate dehydrogenase (G6PDH) forantibody binding sites. The enzyme conjugate activity decreases uponbinding to the antibody. The unbound enzyme conjugate converts oxidizednicotinamide adenine dinucleotide (NAD+) in the Antibody Reagent to NADHand the change in the absorbance can be measured spectrophotometricallyat 340 nm. Enzyme activity decreases upon binding to the antibody,allowing analyte concentrations in a sample to be measured in terms ofG6PDH activity.

EMIT® immunoassays have been developed for screening an individual drugor a class of drugs.

In many cases it is desirable to be able to detect multiple analyteswith a single assay. This is relevant e.g. when screening subjects foruse of different drugs or simultaneously detecting a drug and its drugmetabolites to increase the time window in which drug use can bedetected.

U.S. Pat. No. 7,560,239 discloses a composition wherein differentanalytes are conjugated to G6PDH via amine groups on the G6PDH moleculein a one step reaction. However, conjugating two different analytes toG6PDH via amine chemistry does not allow precise control of the ratio ofthe two different analytes and may result in loss of enzymatic activity.

OBJECT OF THE INVENTION

The technical problem underlying the present invention is to provideimproved G6PDH conjugates, methods of their preparation and their usefor detection of multiple analytes.

SUMMARY OF THE INVENTION

Before the invention is described in detail, it is to be understood thatthis invention is not limited to the particular component parts or theprocess steps of the methods described as such methods may vary. It isalso to be understood that the terminology used herein is for purposesof describing particular embodiments only, and is not intended to belimit-ing. It must be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include singularand/or plural referents unless the context clearly dictates otherwise.It is also to be understood that plural forms include singular and/orplural referents unless the context clearly dictates otherwise. It ismoreover to be understood that, in case parameter ranges are given whichare delimited by numeric values, the ranges are deemed to include theselimitation values.

The invention relates to a composition which comprises at least twodistinct specific binding pair (sbp) members conjugated to aglucose-6-phosphate dehydrogenase (G6PDH), wherein at least a firstspecific binding pair member is conjugated to G6PDH via a thiol groupand wherein at least a further specific binding pair member isconjugated to G6PDH via a amino group.

The composition of the invention can be used to detect both related orsimilar compounds and unrelated or dissimilar compounds in a homogeneousimmunosassay format. For example it could be desired to detect a drugand an analyte of said drug to increase the time window wherein the drugor its metabolite can be detected in a subject. On the other hand itcould be desired to simultaneously detect a plurality of unrelatedanalytes in a single assay, e.g. detection of a variety of drugs forscreening a subject for drug abuse. The first and further binding paircan therefore be strucuturally similar/related or structurallydifferent/unrelated. Further, the first and further binding pair can beserologically cross-reactive or not cross-reactive.

According to an aspect of the invention, the G6PDH is a mutant G6PDH,the mutant G6PDH being derived from a precursor G6PDH by the insertionof at least one cysteine per subunit, or substitution of at least oneamino acid with cysteine per subunit, as compared to the precursorG6PDH.

According to an aspect of the invention, G6PDH is a bacterial G6PDHderived from the genus of bacterium selected from the group consistingof Leuconostoc.

Mutant G6PDH which can be used in the compositions and methods of theinvention are decribed in U.S. Pat. No. 6,455,288, U.S. Pat. No.6,033,890, and U.S. Pat. No. 6,090,567 each of which is hereinincorporated by reference in its entirety.

According to an aspect of the invention, the two distinct binding pairmembers are serologically not cross reactive.

According to an aspect of the invention, the composition comprises threeor more distinct specific binding pair (sbp) members conjugated toG6PDH.

According to an aspect of the invention, the composition comprises aplurality of distinct further specific binding pair members conjugatedto a respective plurality of amino groups.

According to an aspect of the invention, the composition comprises aplurality of distinct first specific binding pair members conjugated toa respective plurality of thiol groups.

According to an aspect of the invention, the first and second specificbinding pair members are selected from the group consisting of opium,opioid analgesics, amphetamines, cocaine, methadone, alkaloids,catecholamines, methylendioxyamphetamines (MDMA, MDA, and MDEA, etc.),PCP, propoxyphene, methaqualone, barbiturates, benzodiazepines,tricyclic antidepressants, tranquilizers, tetrahydrocannabinol, LSD,ketamine, GHB, and other drugs of abuse, including amino acids,hormones, and steroids, buprenorphine, norbuprenorphine, and analogs,metabolites, and derivatives thereof.

According to an aspect of the invention, the composition comprises alinker between G6PDH and either or both of specific binding pair memberand further specific binding pair member.

The linker usually comprises a chain of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,11, or 12 atoms, e.g., from about 3 to about 8 atoms, or e.g. from about4 to about 7 atoms, each independently selected from the group normallyconsisting of carbon, oxygen, sulfur, nitrogen, halogen and phosphorous,and so forth. The linking group may be aliphatic or aromatic. Whenheteroatoms are present, oxygen will usually be present as oxo or etherbonded to carbon; sulfur is usually present as a thioether or otherfunctionality that corresponds to an analogous oxygen functionality;nitrogen is usually present as nitro, nitroso or amino, normally bondedto carbon; phosphorous is usually bonded to carbon, sulfur, oxygen ornitrogen, usually as phosphonate and phosphate mono- or diester. Commonfunctionalities in forming a covalent bond between the linker and themolecule to be conjugated, namely, enzyme or analyte, includealkylamine, amidine, thioamide, ether, urea, thiourea, halogen,isothiocyanate, guanidine, azo, thioether and carboxylate, sulfonate,and phosphate esters, amides and thioesters.

The invention further relates to a method for producing a composition ofthe invention, comprising the steps of:

conjugating a first specific binding pair member to G6PDH via a thiolgroup; and then

conjugating at least a further specific binding pair member to G6PDH viaa amino group.

According to an aspect of the invention, the step of conjugatingincludes providing a linker between G6PDH and either or both of specificbinding pair member and further specific binding pair member.

The invention further relates to a method of detecting a first analyteand a further analyte in a sample, comprising the steps of:

-   (i) combining in a liquid medium:-   (a) said sample,-   (b) a composition comprising G6PDH wherein a first specific binding    pair member is conju-gated to G6PDH via a thiol group and a further    specific binding pair member is conjugated to G6PDH via an amino    group,-   (c) a first antibody capable of binding the first specific binding    pair member,-   (d) a further antibody capable of binding the further specific    binding pair member, and-   (e) a substrate for said G6PDH; and-   (ii) determining the enzymatic activity of said G6PDH in said    medium.

Enzymatic activity can be determined by using a suitable signalproducing system.

The analytes of interest include, but are not limited to drugs,metabolites, pesticides, pollutants, and the like. Included among drugsof interest are the alkaloids.

Among the alkaloids are morphine alkaloids, which includes morphine,codeine, heroin, dextroamphetamine, their derivatives and metabolites;cocaine alkaloids, which include cocaine and benzoyl ecgonine, theirderivatives and metabolites, ergot alkaloids, which include thediethylamide of lysergic acid; steroid alkaloids; iminazoyl alkaloids;quinazoline alkaloids, isoquinoline alkaloids; quinoline alkaloids,which include quinine and quinidine; diterpene alkaloids, theirderivatives and metabolites. Analytes of particular interest includeopium, opioid analgesics, amphetamines, cocaine, methadone, alkaloids,catecholamines, methylendioxyamphetamines (MDMA, MDA, and MDEA, etc.),PCP, propoxyphene, methaqualone, barbiturates, benzodiazepines,tricyclic anti-depressants, tranquilizers, tetrahydrocannabinol, LSD,ketamine, GHB, and other drugs of abuse, including amino acids,hormones, and steroids, buprenorphine, norbuprenorphine,and analogs,metabolites, and derivatives thereof.

Definitions

Before proceeding further with the description of the specificembodiments of the invention, a number of terms will be defined. Unlessdefined otherwise, technical and scientific terms used herein have thesame meaning as commonly understood by one of ordinary skill in the artto which this invention belongs.

In the context of the present invention, an analyte is a compound orcomposition to be measured, the material of interest. The analyte is amember of a specific binding pair (sbp) and may be a ligand, which ismono- or polyvalent, usually antigenic or haptenic, and is a singlecompound or plurality of compounds which share at least one commonepitopic or determinant site.

In the context of the present invention, a sample which is reasonablysuspected of containing analyte can be analyzed by the method of thepresent invention. Such samples can include human, animal or man-madesamples. The sample can be prepared in any convenient medium which doesnot interfere with the assay. Typically, the sample is an aqueoussolution or a natural fluid, preferably, urine, whole blood, serum,plasma, cerebral-spinal fluid, or saliva more preferably, serum. Thesample source can also be hair or tissue.

The term glucose-6-phosphate dehydrogenase or “G6PDH” refers to theenzyme glucose-6-phosphate dehydrogenase, which may be obtained eitherfrom natural sources, such as from yeast, bacteria, in native ormutational form or prepared by recombinant methods.

A “precursor G6PDH” means a naturally occurring G6PDH enzyme as well asa recombinant G6PDH enzyme having a sequence substantially identical toa naturally occurring G6PDH.

The amino acid sequence of a G6PDH mutant is derived from the precursorG6PDH amino acid sequence by the substitution or deletion of one or moreamino acids of the precursor amino acid sequence or the insertion of oneor more amino acids into the precursor amino acid sequence. Suchmodification can be achieved by recombinant modification of theprecursor DNA sequence which encodes the amino acid sequence of theprecursor G6PDH rather than manipulation of the precursor G6PDH enzymeper se. The techniques of DNA recombinant engineering are known in theart.

In the context of the present invention, measuring the amount of ananalyte comprises quantitative, semiquantitative, and qualitativemethods as well as all other methods for determining analyte. Forexample, a method which merely detects the presence or absence ofanalyte in a sample suspected of containing an analyte is considered tobe included within the scope of the present invention. Synonyms for thephrase “measuring the amount of analyte” which are contemplated withinthe scope of the present invention include, but are not limited to,detecting, measuring, or determining analyte; detecting, measuring, ordetermining the presence of analyte; and detecting, or determining theamount of analyte.

In the context of the present invention, a member of a specific bindingpair (sbp member) is one of two different molecules, having an area onthe surface or in a cavity which specifically binds to and is therebydefined as complementary with a particular spatial and polarorganization of the other molecule. The members of the specific bindingpair are referred to as ligand and receptor (antiligand), sbp member andsbp partner, or the like. These will usually be members of animmunological pair such as antigen-antibody.

A ligand is any organic compound for which a receptor naturally existsor can be prepared. For example, in one context of the presentinvention, the analyte is a ligand and the present invention providesmethods for determining the concentration of the analyte which is aligand.

An analog of a ligand, of an analyte or of a member of a specificbinding pair (sbp member) is modified ligand or ligand surrogate,modified analyte or analyte surrogate, or modified sbp member or sbpmember surrogate which can compete with the analogous ligand, analyte orsbp member for a receptor, antiligand, sbp partner, or the like, themodification providing means to join a ligand analog, analyte analog, orsbp member analog to another molecule. The ligand analog, analyteanalog, or sbp member analog will usually differ from the ligand,analyte, or sbp member by more than replacement of a hydrogen with abond which links the ligand analog, analyte analog, or sbp member analogto a hub or label, but need not.

A receptor is any compound or composition capable of recognizing aparticular spatial and polar organization of a molecule. These organizedareas of a molecule are referred to as epitopic or determinant sites.Illustrative naturally occurring receptors include antibodies andenzymes.

A linker or a linking group is a portion of a structure which connects 2or more substructures. A linking group has at least 1 uninterruptedchain of atoms extending between the substructures. The atoms of alinking group are themselves connected by chemical bonds.

A conjugate is a molecule comprised of two or more substructures boundtogether, optionally through a linking group, to form a singlestructure. The binding can be made either by a direct connection (e.g. achemical bond) between the subunits or by use of a linking group. Withinthe context of the present invention, a conjugate is a G6PDH enzymeattached to a hapten, sbp member or analyte analog.

Conjugation is any process wherein two moieties, chemical structures, ormolecules are linked together to form a conjugate. The conjugationprocess can be comprised of any number of steps.

Haptens are capable of binding specifically to corresponding antibodies,but usually do not themselves act as immunogens for preparation of theantibodies. Antibodies which recognize a hapten can be prepared againstcompounds comprised of the hapten linked to an immunogenic carrier.

The signal producing system is utilized in assays for analytes and mayhave one or more components, at least one component being a mutantG6PDH. The signal producing system generates a signal that relates tothe presence or amount of analyte in a sample. The signal producingsystem includes all of the reagents required to produce a measurablesignal.

Other components of the signal producing system can include substrates,enhancers, activators, chemiluminescent compounds, cofactors,inhibitors, scavengers, metal ions, specific binding substances requiredfor binding of signal generating substances, coenzymes, substances thatreact with enzymic products, other enzymes and catalysts, and the like.

The signal producing system provides a signal detectable by externalmeans, normally by measurement of electromagnetic radiation, desirablyby visual examination. For the most part, the signal producing systemincludes a chromophoric substrate and mutant G6PDH enzyme of theinvention, where chromophoric substrates are enzymatically converted todyes which absorb light in the ultraviolet or visible region.

Various ancillary materials will frequently be employed in an assay inaccordance with the present invention. For example, buffers willnormally be present in the assay medium, as well as stabilizers for theassay medium and the assay components. Frequently, in addition to theseadditives, additional proteins may be included, such as albumins, orsurfactants, particularly non-ionic surfactants, binding enhancers,e.g., polyalkylene glycols, or the like.

Incorporation by Reference

All publications and patent applications cited herein are incorporatedby reference as if each individual publication or patent applicationwere specifically and individually indicated to be incorporated byreference.

DETAILED DESCRIPTION OF THE INVENTION

Additional details, features, characteristics and advantages of theobject of the invention are further disclosed in the followingdescription and figures of the respective examples, which, in anexemplary fashion, show preferred embodiments of the present invention.However, these examples should by no means be understood as to limit thescope of the invention.

In the attached Figures,

FIG. 1 schematically shows the chemical structure of embodiments ofcompositions according to the invention,

FIG. 2 shows the structure of the exemplary analytes MDMA, MDA and MDEA,

FIG. 3 shows an exemplary synthesis scheme for obtaining an embodimentof a composition according to the invention, showing the synthesis ofMDA/amphetamine mutant G6PDH conjugate (7),

FIG. 4 shows an exemplary synthesis scheme for obtaining an embodimentof a composition according to the invention, showing the synthesis ofMDA/Methamphetamine mutant G6PDH conjugate (9)

FIG. 5 shows an exemplary synthesis scheme for obtaining an embodimentof a composition according to the invention, showing the synthesis ofMDA/Amphetamine/Methamphetamine mutant G6PDH conjugate(10),

FIG. 6 shows a response curve for detection of ecstasy, MDA, MDEA,methamphetamine and amphetamine using a composition according to theinvention,

FIG. 7 shows a response curve for detection of ecstasy, MDA, MDEA,methamphetamine and amphetamine using a composition according to theinvention,

FIG. 8 shows a response curve for detection of ecstasy, MDA, MDEA,methamphetamine and amphetamine using a composition according to theinvention,

Homogeneous enzyme immunoassays depend on the availability of enzyme-sbpmember conjugates whose enzyme activity can be strongly modulated onbinding of the sbp partner. The present invention provides enzyme-sbpmember conjugates which can bind to and detect multiple differentanalytes for conducting assays that are useful in homogeneousimmunoassays.

The compositions of the invention with multiple detection capability inEMIT®format need to satisfy some basic conditions: 1) different types ofhaptens (molecules) require to be immobilized into the G6PDH to make onemulti-hapten-G6PDH conjugate; 2) the multi- hapten-G6PDH conjugate needsto be recognized by its corresponding antibody(ies) in order to generateenzymatic inhibition and therefore detection of multiple drugs; 3) themulti-hapten-G6PDH conjugate should retain its enzymatic activity. Basedon these conditions, mutant G6PDH was selected as an excellent templateto make the new multi-hapten-G6PDH conjugate. Both thiol and aminefunctional groups on G6PDH are utilized for immobilization of differenthaptens.

A suitable mutant G6PDH for example is G6PDH from Leuconostocmesenteroides (e.g. ATCC 12291) carrying one or several of the followingmutations:

-   Ala-45-Cys-   Arg-46-Cys-   Gln-47-Cys-   Ala-48-Cys-   Leu-49-Cys-   Asn-50-Cys-   Asp-51-Cys-   Asp-52-Cys-   Glu-53-Cys-   Phe-54-Cys-   Lys-55-Cys-   Gln-56-Cys-   Leu-57-Cys-   Val-58-Cys-   Arg-59-Cys-   Asp-60-Cys-   Lys-128-Cys-   Lys-182-Cys

The entire amino acid sequence of the wild type G6PDH from Leuconostocmesenteroides is given below and in references 12, 13, and 14:

VSEIKTLVTF FGGTGDLAKR KLYPSVFNLY KKGYLQKHFAIVGTARQALN DDEFKQLVRD SIKDFTDDQA QAEAFIEHFSYRAHDVTDAA SYAVLKEAIE EAADKFDIDG NRIFYMSVAPRFFGTIAKYL KSEGLLADTG YNRLMIEKPF GTSYDTAAELQNDLENAFDD NQLFRIDHYL GKEMVQNIAA LRFGNPIFDAAWNKDYIKNV QVTLSEVLGV EERAGYYDTA GALLDMIQNHTMQIVGWLAM EKPESFTDKD IRAAKNAAFN ALKIYDEAEVNKYFVRAQYG AGDSADFKPY LEELDVPADS KNNTFIAGELQFDLPRWEGV PFYVRSGKRL AAKQTRVDIV FKAGTFNFGSEQEAQEAVLS IIIDPKGAIE LKLNAKSVED AFNTRTIDLGWTVSDEDKKN TPEPYERMIH DTMNGDGSNF ADWNGVSIAWKFVDAISAVY TADKAPLETY KSGSMGPEAS DKLLAANGDA WVFKG

In analogy, further suitable mutant forms of G6PDH are derived fromother strains of Leuconostoc mesenteroides, from strains of Leuconostoccitreum (e.g. strain NCIMB 3351), Leuconostoc lactis (e.g. strain NCDO546), and Leuconostoc dextranicum (e.g. strain ATCC 19255). Suitablemutatuions include the insertion of at least one cysteine per subunit,or substitution of at least one amino acid with cysteine per subunit, ascompared to the precursor G6PDH. In particular, suitable mutant forms ofG6PDH include mutations wherein a respective amino acid in a precursorG6PDH molecule derived from Leuconostoc is substituted by cystein at anyof the positions 45 to 60.

The reagent formulation is a two-step reaction. First, two haptens areattached to the G6PDH (Schemes 1-3) using the thiol chemistry in acontrolled manner. Second, different types of haptens can be immobilizedusing the amine chemistry. Our approaches are different from that of theexisting multi-hapten conjugate (reference 11) in which only aminechemistry was used. Based on existing data, using the amine functionalgroups for immobilization of haptens could lead to reduction of theenzymatic activity. This means that only limited amine groups can beused for the attachment of haptens in order to maintain good enzymaticactivity for the EMIT®format. Consequently, using amine chemistry onlyfor preparation of multi-hapten-G6PDH conjugate could limit the amountof hapten on the conjugate in order to maintain good enzymatic activity.

In our approaches, multi-hapten-mutant G6PDH was prepared using thethiol function groups on the enzyme as the first step reaction. Theresulting conjugate retains most of its enzymatic activity 95%). Thiscould be an advantage in that more haptens can be attached to the aminegroups in the second step reaction, while still maintaining goodenzymatic activity. Therefore, applying both thiol and amine chemistryin preparation of multi-hapten-G6PDH should result in a conjugate thathas more hapten loading capacity for the detection of multiple analytes.Without wishing to be bound by this theory, the beneficial effect ofutilizing thiol chemistry in thee compositions and methods of theinvention could be explained as follows: Utilization of thiol chemistryto could result in more stable. Cystein residues can be used that aredistanced from the active site of the enzyme e. In that regard, haptenconjugation through linkage of cysteine may have little or no impact onthe stability of the active quaternary structure that is crucial for theenzymatic activity. This is supported by the observation that mutantG6PDH-hapten conjugates retain very good enzymatic.

There are many analytes, e.g.drugs, that can be used to preparemulti-hapten-G6PDH and test its performance. Three widely abused drugs,amphetamine, methamphetamine and ecstasy were selected as exemplaryanalytes. With this in mind, multi-hapten-G6PDH (7, 9, 10) was preparedas described in Schemes 1-3 and the experimental section. Twomulti-hapten-G6PDHs (7, 9) were used to investigate their multi-drugdetection capability in the EMIT® format. Results were discussed in thefollowing section.

In these approaches, multi-hapten-mutant G6PDH was prepared using thethiol function groups on the enzyme as the first step reaction. Theresulting conjugate retains most of its enzymatic activity 95%). Thiscould be an advantage in that more haptens can be attached to the aminegroups in the second step reaction, while still maintaining goodenzymatic activity. Therefore, applying both thiol and amine chemistryin preparation of multi-hapten-G6PDH should result in a conjugate thathave more hapten loading capacity for the detection of multipleanalytes.

EMIT®Assay Principle:

The Emit® II Plus Assay is a homogeneous enzyme immunoassay. It is basedon competition between drug in the sample and drug-labeled withglucose-6-phosphate dehydrogenase (G6PDH) for antibody binding sites.The enzyme conjugate activity decreases upon binding to the antibody.The unbound enzyme conjugate converts the oxidized nicotinamide adeninedinucleotide (NAD) in the Antibody Reagent to NADH and the change in theabsorbance can be measured spectrophotometrically at 340 nm. Enzymeactivity decreases upon binding to the antibody, allowing analyteconcentrations in a sample to be measured in terms of G6PDH activity.

Testing is carried out using the SYVA®30-R analyzer Syva-30R , S/NA3562011 , available from Siemens Healthcare Diagnostics Inc., NewarkDE. The instrument is employed using EMIT® immunoassay technology. Inthe embodiment of the EMIT® method used herein and discussed in moredetail below, competition between ecstasy and/oramphatemine/methamphetamine analogs on G6PDH conjugates and free drugsin patient samples for antibody binding sites is utilized to determinethe amount of ecstasy and/or amphetamine/methamphetamine in patientsamples. The enzymatic activity of the free conjugate is measured and isdirectly proportional to the amount of drugs in the patient sample.

EMIT®Assay Results:

Conclusion: Multi-hapten G6PDH conjugates (7, 9, 10) were successfullyprepared using mutant G6PDH with both thiol and amine chemistry. Themulti-hapten conjugates (7, 9) were used to produce response curves forthe multianalyte of Amphetamine, Methamphetamine, MDMA, MDE and MDEA.The response for each drug can be modulated by changing the conjugateratios. This concept can be applied to any multi-analyte detectionformat including EMIT®format.

Experimental Section:

Reagents

1) Antibody Reagent: The amphetamine, methamphetamine and Ecstasyantibodies were formulated in the antibody reagent 1 diluent by spikingat concentrations of 45 ug.mL, 7 ug/mL and (1:250) respectively.

2) Conjugate reagent 2: Conjugate lot #7 and #9 (50:50) were formulatedseparately in the reagent 1 diluent at an Rmax of 750 mA/min. Theconjugate solutions were mixed at different ratios (Vol:Vol).

3) Standards/Calibrators: Amphetamines, Methamphetamines, Ecstasy(MDMA), MDA and MDEA standards were prepared at concentrations of 0-1000ng/mL

4) Protocol:

-   Antibody reagent 1=210 uL,-   Conjugate Reagent 2=90 uL-   Sample size=5 uL-   First Wavelength: 340 nm-   Second Wavelength: 412 nm

Instrument: Syva-30-R analyzer S/N A3562011

Preparation of mutant G6PDH (1)

The mutant G6PDH (1) were invented and prepared as described inreferences 1-3.

Preparation of mutant MDA-G6PDH Conjugate (3)

The hapten (2) and its mutant G6PDH Conjugate (3) were prepared asdescribed in reference 4.

Preparation of MDA/Amphetamine Mutant G6PDH Conjugate (7)

Functionization of G6PDH Conjugate (3)

MDA-G6PDH conjugate (3) in pH 7.0 sodium phosphate buffer (5 mL at 1mg/mL) is buffer exchanged in a stirred ultra-filtration cell (10 mL)with 55 mM Tris•HCl, pH 8.0 buffer three times. Final enzyme collectedis 1.0 mL with a concentration of 5.0 mg/mL. To buffer exchanged G6pDHconjugate in 4° C. are added D-glucose 6-phosphate disodium salt hydrate(Sigma, G7250, 30 mg) and NADH (β-NADH disodium salt, USB, Cat. 15345,30 mg), pH of the solution is checked and found to be 8. To thissolution is added 50 μL succinimidyl bromoacetate (4, MolecularBioscience, Cat. 22080, mw: 237.0, 5 mg/mL in DMF) in an ice-water bath.The enzyme solution is stirred in cold room for 45 minutes then dialyzedwith 1 L of 55 mM Tris HCl, pH 8.0 buffer, exchanged with fresh bufferfive times with three hours between each fresh buffer. The dialyzedenzyme solution (5) collected is 2.1 mL with a concentration of 2.45mg/mL.

Reduction of Amphetamine Hapten Linker with TCEP

30 mL of carbitol (Diethylene glycol monoethyl ether, Sigma, D1265-1L)and 20 mL of 20 mM of Sodium acetate pH 4.5 buffer are degassed bybubbling nitrogen through each solution for 15 minutes before theaddition of amphetamine hapten. To amphetamine hapten (MW 314.47, 10.4mg) in a small flask are added degassed carbitol (0.4368 ml) and sodiumactate (20 mM, pH 4.5, 0.2184 mL). The reaction mixture is stirred undernitrogen atmosphere. TCEP HCl (Sigma, C4706, MW 286.65, 11.8 mg, 1.24equivalent of amphetamine hapten) is added into amphetamine haptensolution. The progress of the reaction is monitored by TLC (10.5 mlCH₂Cl₂/4 mL MeOH/0.25 mL acetic acid) and product (6) is a spot lesspolar than that of amphetamine hapten and stained bright yellow withEllman's Reagent. The reaction finishes within one hour.

MDA G6PDH Conjugatate with Amphetamine

MDA-G6PDH deactivated conjugate (5) is bubbled with nitrogen for 30minutes in an ice-water bath, amphetamine-SH hapten (6, 117 μL) is addedinto the conjugate in an ice water bath drop wise through a syringeunder nitrogen atmosphere. The reaction mixture is stirred in a coldroom overnight. MDA-G6PDH-amphetamine conjugate is loaded onto apre-equilibrated G-50 Sephadex column with 55 mM Tris HCl buffer (0.1%NaN₃, pH 8.0), eluted with same buffer. Fractions containing theconjugate (7) are pooled and concentration of the protein is determinedby UV at 280 nm. The concentration of the conjugate (7) is determined tobe 0.43 mg/ml (11.7 mL) by absorbance at 280 nm.

Preparation of MDA/Methamphetamine Mutant G6PDH Conjugate (9):

Functionization of G6PDH Conjugate (3)

MDA-G6PDH conjugate (3) in pH 7.0 sodium phosphate buffer (4.6 mL at 1mg/mL) is buffer exchanged in a stirred ultra-filtration cell (10 mL)with 55 mM Tris.HCl, pH 8.0 buffer three times. Final enzyme collectedis 0.9 mL with a concentration of 5.0 mg/mL. To buffer exchanged G6pDHconjugate in 4° C. are added D-glucose 6-phosphate disodium salt hydrate(Sigma, G7250, 27.6 mg) and NADH (β-NADH disodium salt, USB, Cat. 15345,27.6 mg), pH of the solution is checked and found to be around 8. Tothis solution is added 46.0 μL succinimidyl bromoacetate (4, MolecularBioscience, Cat. 22080, mw: 237.0, 5 mg/mL in DMF) in an ice-water bath.The enzyme solution is stirred in cold room (4° C.) for 45 minutes anddialyzed with 1 L of 55 mM Tris HCl, pH 8.0 buffer, exchanged with freshbuffer five times with three hours between each fresh buffer. Dialyzedenzyme solution (5) collected is 2.5 mL with a concentration of 2.44mg/mL.

Reduction of Methyl Amphetamine Hapten Linker with TCEP

30 mL of carbitol (Diethylene glycol monoethyl ether, Sigma, D1265-1L)and 20 mL of 20 mM of Sodium acetate pH 4.5 buffer are degassed bybubbling nitrogen through for 15 minutes before the addition of methylamphetamine hapten. To methyl amphetamine hapten (MW 360.58, 11.9 mg) ina small round bottomed flask are added degassed carbitol (0.4998 ml) andsodium acetate (20 mM, pH 4.5, 0.2499 mL). The reaction mixture isstirred under nitrogen atmosphere. TCEP HCl (Sigma, C4706, MW 286.65,12.77 mg, 1.35 equivalent of methyl amphetamine hapten) is added intothe methyl amphetamine hapten solution. The progress of the reaction ismonitored by TLC (10.5 ml CH₂Cl₂/4 mL MeOH/0.25 mL acetic acid) andproduct (8) is a spot less polar than that of methyl amphetamine haptenand stained bright yellow with Ellman's Reagent. The reaction finishesin one hour.

MDA G6PDH Conjugate with Methyl amphetamine

MDA-G6PDH deactivated conjugate (5, 2.25 mL) is bubbled with nitrogenfor 30 minutes in an ice-water bath, methyl amphetamine-SH hapten (8,155 μL) is added into the conjugate in an ice water bath drop wisethrough a syringe under nitrogen atmosphere. The reaction mixture isstirred in a cold room (4° C.) overnight. MDA-G6PDH-methyl amphetamineconjugate is loaded onto a pre-equilibrated G-50 Sephadex column with 55mM Tris HCl buffer (0.1% NaN₃, pH 8.0), eluted with same buffer.Fractions containing the conjugate (9) are pooled and the concentrationof the protein is determined to be 0.48 mg/ml (8.88 ml) by UV at 280 nm.

Preparation of MDA/Amphetamine/Methamphetamine Mutant G6PDH Conjugate(10):

Functionization of G6PDH Conjugate (3)

MDA-G6PDH conjugate (3) in sodium pH 7.0 phosphate buffer (15 mL at 1mg/mL) is buffer exchanged in a stirred ultra-filtration cell (50 mL)with 55 mM Tris.HCl, pH 8.0 buffer three times. Final enzyme collectedis 3.0 mL with a concentration of 5.0 mg/mL. To buffer exchanged G6pDHconjugate in 4 ° C. are added D-glucose 6-phosphate disodium salthydrate (Sigma, G7250, 90.2 mg) and NADH (β-NADH disodium salt, USB,Cat. 15345, 90.1 mg), pH of the solution is checked and found to bearound 8. To this G6PDH conjugate solution is added 150.0 μLsuccinimidyl bromoacetate (4, Molecular Bioscience, Cat. 22080, mw:237.0, 5 mg/mL in DMF) in an ice-water bath. The solution is stirred incold room (4° C.) for 45 minutes. The enzyme solution is dialyzed with 1L of 55 mM Tris HCl, pH 8.0 buffer, exchanged with fresh buffer fivetimes with three hours between each fresh buffer. Dialyzed enzymesolution (5) collected is 6.7 mL with a concentration of 4.52 mg/mL.

Reduction of Methyl Amphetamine / Amphetamine Hapten Linkers with TCEP

30 mL of carbitol (Diethylene glycol monoethyl ether, Sigma, D1265-1L)and 30 mL of 20 mM of Sodium acetate pH 4.5 buffer are degassed bybubbling nitrogen through for 15 minutes before the addition of hapten.To methyl amphetamine hapten (MW 360.58, 10.4 mg) in a small roundbottomed flask are added degassed carbitol (0.4368 ml) and sodiumacetate (20 mM, pH 4.5, 0.2184 mL). The reaction mixture is stirredunder nitrogen atmosphere. TCEP HCl (Sigma, C4706, MW 286.65, 11.16 mg,1.35 equivalent of methyl amphetamine hapten) is added into methylamphetamine hapten solution. The progress of the reaction is monitoredby TLC (10.5 ml CH₂Cl₂/4 mL MeOH/0.25 mL acetic acid) and product (8) isa spot less polar than that of methyl amphetamine hapten and stainedbright yellow with Ellman's Reagent. The reaction finishes in one hour.At the same time, to amphetamine hapten (MW 314.47, 7.5 mg) in a smallround bottomed flask are added degassed carbitol (0.3150 mL) and NaOAc(20 mM, pH 4.5, 0.1575 mL). The solution is stirred under nitrogenatmosphere; TCEP HCl (Sigma, C4706, MW 286.65, 9.23 mg, 1.35 equivalentof amphetamine hapten) is added into amphetamine hapten solution. Theprogress of the reaction is monitored by TLC (10.5 ml CH₂Cl₂/4 mLMeOH/0.25 mL acetic acid) and product (6) is a spot less polar than thatof methyl amphetamine hapten and stained bright yellow with Ellman'sReagent. The reaction finishes in one hour.

MDA G6PDH Conjugate with Methyl amphetamine and Amphetamine

MDA-G6PDH deactivatd conjugate (5, 1.8 mL, 4.52 mL) is bubbled withnitrogen for 30 minutes in an ice-water bath, methyl amphetamine-SHhapten (8, 65.5 μL) and amphetamine-SH hapten (6, 57.1 μL) (molar ratioof methyl amphetamine hapten and amphetamine hapte is 1 to 1) are addedinto the MDA G6PDH deactivated conjugate in an ice water bath drop wisethrough a syringe under nitrogen atmosphere. The reaction mixture isstirred in a cold room overnight. MDA-G6PDH-methyl amphetamine/methylamphetamine conjugate is loaded onto a pre-equilibrated G-50 Sephadexcolumn with 55 mM Tris HCl buffer (0.1% NaN₃, pH 8.0), eluted with samebuffer. Fractions containing the conjugate (10) are pooled andconcentration of the protein is determined to be 0.44 mg/ml (11.8 ml) byUV at 280 nm.

REFERENCES

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1. A composition which comprises at least two distinct specific bindingpair (sbp) members conjugated to a glucose-6-phosphate dehydrogenase(G6PDH), wherein at least a first specific binding pair member isconjugated to G6PDH via a thiol group and wherein at least a furtherspecific binding pair member is conjugated to G6PDH via a amino group.2. The composition according to claim 1, wherein the G6PDH is a mutantG6PDH, the mutant G6PDH being derived from a precursor G6PDH by theinsertion of at least one cysteine per subunit, or substitution of atleast one amino acid with cysteine per subunit, as compared to theprecursor G6PDH.
 3. The composition according to claim 1, wherein G6PDHis a bacterial G6PDH derived from the genus of bacterium selected fromthe group consisting of Leuconostoc.
 4. The composition according toclaim 1, wherein the two distinct binding pair members are serologicallynot cross-reactive.
 5. The composition according to claim 1, comprisingthree or more distinct specific binding pair (sbp) members conjugated toG6PDH.
 6. The composition according to claim 1, comprising a pluralityof distinct further specific binding pair members conjugated to arespective plurality of amino groups.
 7. The composition according toclaim 1, comprising a plurality of distinct first specific binding pairmembers conjugated to a respective plurality of thiol groups.
 8. Thecomposition according to claim 1, wherein the first and second specificbinding pair members are selected from the group consisting of opium,opioid analgesics, amphetamines, cocaine, methadone, alkaloids,catecholamines, methylendioxyamphetamines (MDMA, MDA, and MDEA, etc.),PCP, propoxyphene, methaqualone, barbiturates, benzodiazepines,tricyclic antidepressants, tranquilizers, tetrahydrocannabinol, LSD,ketamine, GHB, and other drugs of abuse, including amino acids,hormones, and steroids, buprenorphine, norbuprenorphine, and analogs,metabolites, and derivatives thereof.
 9. The composition according toclaim 1, further comprising a linker between G6PDH and either or both ofspecific binding pair member and further specific binding pair member.10. The composition according to claim 1, wherein the first binding pairmember is MDA or an analog, metabolites, or derivative thereof and thesecond binding pair member is Amphetamine or an analog, metabolite, orderivative thereof or Methamphetamine or an analog, metabolite, orderivative thereof.
 11. The composition according to claim 10, whereinthe first binding pair member is MDA or an analog, metabolites, orderivative thereof and the second binding pair member is Amphetamine oran analog, metabolite, or derivative thereof and a third binding pairmember is Methamphetamine or an analog, metabolites, or derivativethereof.
 12. A method for producing a composition according to claim 1,comprising the steps of: conjugating a first specific binding pairmember to G6PDH via a thiol group; and then conjugating at least afurther specific binding pair member to G6PDH via a amino group.
 13. Themethod according to claim 12, wherein the step of conjugating includesproviding a linker between G6PDH and either or both of specific bindingpair member and further specific binding pair member.
 14. A method ofdetecting a first analyte and a further analyte in a sample, comprisingthe steps of: (i) combining in a liquid medium: (a) said sample, (b) acomposition comprising G6PDH wherein a first specific binding pairmember is conjugated to G6PDH via a thiol group and a further specificbinding pair member is conjugated to G6PDH via an amino group, (c) afirst antibody capable of binding the first specific binding pairmember, (d) a further antibody capable of binding the further specificbinding pair member, and (e) a substrate for said G6PDH; and (ii)determining the enzymatic activity of said G6PDH in said medium.